He was led away by security after the drink was thrown, as a person believed to be the thrower was dragged away by a police community support officer.
In a video circulating on social media a voice can be heard shouting “fascist!”, as Mr Farage walks away.
“How did you not stop that?” the Brexit Party leader could be heard saying to his security guards.
He was also heard to mutter “complete failure” and “I could have spotted that a mile off” as he was ushered into a taxi.
Paul Crowther, from Throckley, Newcastle, said he had thrown a £5.25 Five Guys banana and salted caramel milkshake at Mr Farage.
He said he saw the Brexit Party event in the city centre and then spotted the politician.
“I didn’t know he was in town. I thought, this is my only chance,” he said. “It’s a right of protest against people like him.
“The bile and the racism he spouts out in this country is far more damaging than a bit of milkshake to his front.”
Mr Crowther spoke to members of the press as he stood handcuffed outside a Waterstones book shop.
“I was quite looking forward to it but I think it went on a better purpose,” he said of the milkshake.
The 32-year-old denied that someone had been cut, saying he had only thrown liquid on the politician. “I do not regret it. It was worth it,” he added.
A social media user under the name “The Mad Brewer” tweeted an image of a milkshake minutes before the attack.
“I’d got my milkshake and coincidentally there’s a Brexit Party march,” the user wrote.
A few minutes later the user tweeted once again. “I f***ing did it, it was Farage, I can’t believe it,” he wrote.
Mr Crowther has not confirmed whether the Twitter account is his personal one.
Mr Farage had just given a short speech at the city’s Grey’s Monument as part of a tour of the country when the drink was thrown.
“Sadly some Remainers have become radicalised, to the extent that normal campaigning is becoming impossible,” the Brexit Party leader tweeted after the incident.
“For a civilised democracy to work you need the losers’ consent, politicians not accepting the referendum result have led us to this.”
Northumbria Police confirmed a 32-year-old man had been arrested on suspicion of common assault.
Mr Benjamin, a far-right activist, has had four milkshakes thrown at him in the space of a week.
Additional reporting by agencies
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